Applicant's novel approach to acoustic beam modification arose in response to the very poor sonic beam directivity of piezo-electric, such as ceramic, transducers for detection of differential diffuse backscatter from small volumns of abnormal cells surrounded by normal cellular structures as the same are now known. At high frequencies, necessary for small cellular volume detection, certain basic acoustic limitations necessitate the maximum possible input and output of sonic energy from such a pulse-reflective system for early stage cancer detection. Properties of the acoustic system must be fine-tuned to detect and differentiate the very weak sonic energy signal contrast between normal and tumorous tissue.
The inventor has confirmed the existence of such signal differences between between tumors and surrounding tissues having forecast this possibility by quantitative studies of comparable time-amplitude graphs of normal and tumorous tissues.
This work was initially done with air-backed quartz transducers working in the near field. Ceramic tranducer materials offered much greater acoustic sensitivity but possessed serious limitations in the beam profile. This limitation was initially overcome by externally focussing the beam with acoustic lenses which resulted in loss of maximum degree of target detectability of diffuse back-scatter which has been found clinically necessary to achieve maximum target sensitivity.
X-cut quartz piezo-electric transducer plates can be designed to produce a highly directive beam of ultrasonic energy, operating as plane piston radiators to produce Gausian Apodization Beams. The quartz Gausian Beam is not uniformly sensitive axially and produces various degrees of maximum and minimum intensity nodes along its length.
Ceramic plates were selected as being more suitable than quartz for the purpose of target identification in human and animal tissues containing abnormal, irregular, disordered cellular structures such as tumors, some of which produce diffuse back-scattered reflection of sonic energy. Ceramic plates were found to be deficient directionally when operated as a plane piston. Current practices use focusing by acoustic lenses to correct this deficiency with resultant loss of maximum sensitivity to clinically desirable, smallest levels of diffuse, back-scattered signal content.
The present invention has solved the problem of poor axial beam directivity of ceramic transducer plates without reducing target sensitivity which are naturally of a much higher order in revealing diffuse back-scattered sonic energy than that of X-cut quartz.
With applicant's invention, the energy receiving or energy input side of the plate has been divided into a number of separate electrodes. When coupled with a suitable electrode backing such as a conducting rubber or elastomeric member, rigid plate, or preferably a relatively soft metallic plate or individual conductor, the electrically energized transducer functions uniquely to produce a parallel beam of uniform intensity throughout the useful range of the beam, with integrity throughout the cross section of the beam and with azimuthal consistency. Applicant has also found the beam to be steerable by selective energization of the electrodes through a variety of excitement modes including integrated ciruit amplifiers with controlled, sequential or simultaneous stimulation of the electrodes.
Such an intensity-uniform beam of ultrasonic energy has been shown experimentally to detect far more back-scatter energy from mammalian tissue. The present state-of-the-art knowledge has sacrificed maximum tissue signal sensitivity in a perceived quest by some designers for essential, including azimuthal or lateral, signal clarity. This developmental trend has not yet resulted in realization of the full potential of ultrasound for tumor detection and diagnosis.
It is therefore an object of the applicant's invention to provide an intrinsically collimated, ultrasonic transducer which provides for a plurality of separately emitted beams acting as a single beam focussed at infinity.
It is a further object of the applicant's invention to provide an intrinsically collimated, ultrasonic transducer which eliminates the requirement of focussing elements for image clarity by obtaining a collimated, parallel beam of energy of total transducer area for the detection of very small cellular tissue abnormalities as compared to a narrow, point focussed beam..
It is a further object of the applicant's invention to produce an intrinsically collimated, ultrasonic transducer having a plurality of electrodes with a conducting, flexible member providing ultrasonic energy to each of its separate electrodes.
It is still a further object of the applicant's invention to produce an intrinsically collimated, ultrasonic transducer which provides a maximal, desired, low energy loss energy transmission at transducer level, into and from human tissues.
It is yet a further object of the applicant's invention to provide an intrinsically collimated ultrasonic transducer which provides a new and novel means for more complete detection and certain, accurate diagnosis of tissue abnormalities.